Telephone system



July 1933.

T. A. LUNDEL Er AL ELEPHONE SYSTEM Filed April 13 1951 2 Sheets-s 1 II I II II T l vc y 1933- 'r. A. LUNDELL El AL. 1,920,089

TELEPHONE SYSTEM Filed April 13, 1931 2 Sheets-Sheet 2.

V i a Patented July 25, 1933 burr sates new orr c 'rons'rniv .enrn runnnnnnnn ronnsnri tnunnun'or scrocirrromzr, swnnnnnssrenone To 'rnrinronnnrrnsonesnr L. m. EEIOSSON, or STOCKHOLM, SWEDEN, A coin- PANY or SWEDEN Application'filed April 13, 1931,861'131 No The present invention relates to automatic telephone systems. More particularly itrelates to such installations in which selector impulses are tobe sent over lines including intermediate repeaters.

lVith a growing automatization of telephone systems it has becomedesirable to be able to send impulses :for the control of selectors over long distance lines, coil-loaded cables, long coil-loaded'junction lines between local exchanges, etc; When using mit voice-frequency alternating currents r with a 11111111111111101? damping and further generally include intermediate repeaters, which amplify passing voice-frequency currents but which, on the other hand, not at all or only with difiiculty let through currents of a higher or a lower frequency. I

A receiver forreceiving such signals must, however, be selective in order not to be actuated by speech currents during the conversation or by disturbance currents. However, this selectivity of the receiver vcannot be obtained without siniult'aneously introducing acertain inertia whereby the recep-. tion of rapld selector impulses s made more- According to. the present invention this difficulty is eliminatedthereby that the receiver isnormally in a selective condition, being unsensitive to talking oscillations in general and particularly also to such talking oscillations which by chance come Within the signal frequency r'ange,but, on the other hand, reacting for call signals or the like of comparatively long duration, the receiver being adapted, upon receiving such signals, to be shifted to a less selective or unselective I i I rnrinrnonri svsrnivr 529,812, and in Sweden January 22,1929.

condition, thereby becoming capable of receiving rapid selector impulses. After completed selecting operation the receiver is again shifted to normal selectivity so that it is prepared, during the conversation, to receive the clearing signal. i

The invention will be more closely described with reference to the accompanying drawings in which Figures 1, 2 and 3 show different embodiments of receivers adapted to receive selector impulses as well as signals and provided with shifting means for shifting from a selective condition to a less selective or an unselective condition, and

vice versa.

In Figure 1 a voice-frequency generator 2, by way of example a valve generator buzzer or the like, is connected to the sending end of the line 1. The current supplied by the generator is controlled by an impulse sender 3, by way of example a finger disc.- To the receivingend of the line is connected an impulse receiver 4, including a rectifying device in which the alternating current impulses are'transformed to direct current impulses. .The latter impulses in turn actuate over a selectively acting device a sequence switch 6. or selectors connected ically represented by a contact arm 7. Said selective device, which in the embodiment according to, Figure 1 is selective with re- 'spect to the duration of the signals, comprises a slow acting relay 40 and a cooperating relay 5, of which relays the former is normally connected to the impulse receiver ,4 over a switch consisting of the contact set of a relay 41. The relay 5, on the other hand, is normally disconnected from the circuit and adapted to be connected to the impulse receiver 4 in place of the relay 40 upon said switch being shifted at the energization of the relay 41. A voicefrequenc-y call signal of, the required duration is transformed in the impulse receiver 4 to a direct current impulse of corresponding duration, the duration being suflicient to bring about the energization of the relay 40 whereby the sequence switch 6' is actusteel and set in a certain position in which thereto, said selectors being diagrammat soon asthe desired connection is establishedit closes the circuit through the relay 11. which attracts its armature, disconnecting the relay 40 and connecting the relay 5 into circuit. Consequently the more rapid selec tor impulses hereafter incoming will actuate the latter relay which thus repeats the selector impulses for setting the selector. As

the currentthrough the relay a1 isinterrupted' due to the shifting of the sequence switch," the shifting device returns to its normal condition, the relay 5 is disconnected from the circuit and the relay 10 again connected to the impulse receiver 1. The device is thus again shifted to a selective con dition, whereby disturbance currents of short duration are prevented from actuating the selectors.

Flgure 2 shows a similar arrangement. The two relays dand 5 1n: Figure 1 alternatively connected into circuitare here replaced by a s ngle relay prov1ded withtwo windings 42, 13 and adapted to be shifted itrom'a slow-acting to a qulch-acting condition by removing a normally existing short circuit on the winding 43. The winding til is permanently connected to the impulse receiver 4; The short circuiting of the wind; 43 takes place at a normally closed con tact of a relay 44: corresponding to the relay 41 in Figure 1 and connected to the sequei'ice switch. in the same manner as said relay. As the relay 412, 13 is 1iormal.l ;"slowacting similarly to the relay 10 in Figure 1 short SI DELlS for instance disturbance cura:

rents, cannot actuate the same. If, on the other hand, a call signal of comparatively long duration is received the relay 12, 13

attracts its armature, wherebythe sequence switch 1s actuatedand 1n thesame manner 1n the above described embodiment closes Ll. D

the circuit through the relay 4d whichfis.

energized, whereby the short circuit .of the winding 18 is removed and the relay d2, shifted from a slow-acting condition to a quick-acting condition, thus becoming capable of responding to the. selector impulses.

After the completion or" the selecting oper ation the relay 441 is de-energized and the coil 13 is again short-circuited, the relay 12, 4-3 becoming again slow-acting andthus selective. y

FigureB'shows an application or thein 'vention inconjunction with a receiving device of the kind described in the Swedish Patent No. 66,958. In this case the impulse receiver 1 consists ofsaidlrnown receiving device which is normally selective with respect. to frequencyand adapted to receive si nalling currents within a certain coniparatively limited .itrequency range but which is, onthe other-hand, normally unsusceptible to other signalling currents. To the output ;side.=of the impulse receiver is connected a direct current relay 5, the con The grid circuit of said valve comprises. two

branch circuits 9, 10 each including the secondarywin'ding of a transformer 11 and 12 respectively, the primary windings of which are series-connected inthe anode circuit of an amplifiervalve 13, the grid circuit of which is connected to thereceiving end of the line 1 through the transformer 14.. Through a battery 15 the valve 13 receives a negative gridbiasing voltage of such a magnitude thatthevalve acts only as an amplifier, A battery 16 supplies current to the. anode: circuit of both valves 8 and 13. The primary windings of the transformers 11, 12 are each provided with a resonance shunt 17 and 18 respectively, tuned to the frequencyof the signalling current. As previously mentioned the same frequency may beusedalso tor the selector impulses. The shunt '17 is arranged for voltage resonance and includes an. inductance and a capacity connected in parallel therewith, whereas the shunt 18 is arranged for current resonance and includes an inductance and a capacity in series. The anode circuit of the valve 15 forms a filter circuit with two seriesconnected filters 17 and 18. The filter transmits to the branch circuit 9 only currents within the frequency range of the circuit 10 by the shunt 18 acting as a short circuit for. said currents.

hen a wave-tram of talking currents, for instance also including talking oscillations of signalling frequency or approximately of signalling frequency,'are received from the lineover the transformer 14; and the amplifier 13 the condenser :in the shunt 1-7 will to begin with act as a short circuit, whereas the shunt 18 acts as a high resistance. For'this reasoncurrents of signalling frequency and short duration will be transmitted to thecircuit 10 together with the other currents but will, on the other hand, leave the. circuit .9substantially unaftected. YVith regard to the signalling frequencies the conditions in the shunt will be reversed: as in this case the shunt 17, as previously mentioned, will offer a high resistance to the signalling currents as soon as a stationary condition of oscillations has been established, whereas the shunt 18 forms a short circuit. The transformer 12 together with the shunt 18 and the branch circuit 10 thusform 'a'blocking device which controls voltage from a battery 26 and 27'respectively, which voltage, however, alone isunsuflicient to make the lamp glow. Thus the glow lamp 19, 20' normally acts as an interruption in the secondary circuits of the transformers 11, 12.

The grid circuit of the valve 8 comprises, in addition to the branch circuits 9, 10, also a third branch 23 in which is included a grid leak 24: shunted with a condenser 25. Through the battery 26;and another battery 26 the grid of the valve 8 obtains a negative grid biasing voltage of such a value that the anode current is practically Zero in the normal condition of the receiving device.

Voltages induced in the circuits 9, 10 through signalling currents and other alternating currents incoming from the outside are superposed upon the direct current voltages impressed upon' the glow lamps 19, 2O

and may, if sufficiently strong, bring the corresponding glow lamp-to glow, whereby a conducting path is established through the lamp. hen the lamp 19 is brought to glow through an incoming signalling current the grid of the valve 8 is connected to the positive pole of the battery 26, the upper coating of the condenser 25 then receiving a positive charge. The grid voltage of the valve 8 is thus increased in a positive direction which results in that a current passes through the winding of the relay 5 bringing the signallingdevice into operation. When the signalling current has ceasedthe condenser 25 is discharged through the grid leak 24 and the valve 8 is restored to its normal position with currentless anode circuit. i

If currents having another frequency than the signalling frequency and, for instance, including only short impulses of signalling frequency are received from the line only the glow lamp 26 is made to glow, the upper coating of the condenser 23 then receiving a negative charge from the battery 27.

remains currentless. If under this condition talking currents having frequencies.

inside the signal frequency The anode circuit of the valve 8 thus- It has been found, however, that in speech the negative charge is favoured to such an extent as compared with the positive one that the latter will never be predominant. This result depends substantially thereupon that the condenser is discharged. comparatively slowly through the leak 24. Its negative charge will therefore be maintained until-other frequencies than signalling frequencies are again predominant, when the condenser 25 is again negatively charged. The condenser 25 should therefore preferably have such a capacity. that it may be charged by means of a small amount of energy and the leak 24 should have such a resistance that one obtains the slow discharge of the condenser required for safe operation of the device.

The arrangement according to Figure 3 has the further advantage that disturbance currents, which usually have only a small energy, do not influence the signal receiver for the reason that weak currents are unable to bring the-glow lamps to glow.

As will be clear from the foregoing t arrangement is very selective wherefore the relay will be unafiected not only by currents outside the signal frequency range but also, on account of the inertia required for.

obtaining the selectivity, also for very short impulses of signalling frequency. To render possible the reception of rapid selector impulsesby means of this special receiver the sequence" switch 6 is provided with a special ring of contacts comprising two oprelay is energized, whereby the blocking device is thus made inoperative. The receiver is thereby shifted to a condition in which it is .more quick acting than before and is now prepared to receive the rapid selector impulses which over the transformer 14, the amplifier 13 and the transformer 11 are transmitted to the circuit 9 which rectifies the same and supplies the rectified voltage impulses to the condenser 25. The valve 8 will now be actuated in the same manner as when pure signalling impulses are received, as previously described. The selector impulses will be repeated by the relay 5, through the contactcircuit of which they are supplied to the selector mechanism. After completedselecting operation the circuit for the relay 30 is interrupted by a signalling current.

further shifting. of the sequence switch 6 whereby the shunt 17 is again closed and the short circuit of the transformer 12 removed. The recelver is thereby restored to its original. "selectlve condition, in whlch 1t sation in orderito be prepared, to receive the with the aid of a high-frequency carrier Wave. Instead of making the signal receiver selective with respect to the frequency or to the duration of the signal one may, in a manner known per se, make the same selective with respect to the WVe claim I 1. In a telephone system'm combination, a

transmission line, means for transmitting signalling currents of voice frequency over said line, a slgnal receiver, means associated with said receiver and responsive to signals of predetermined minimum length i for changing the condition of said receiver from a higher to a lower degree of selectivity so as'to make the receiver responsive to rapid signal impulses. I

2.111 a telephonesystem in combination, a transmission line, means for transmitting signalling currents of voice frequency over said line, a signal receiver, means associated with said receiver and responsive to signals of predetermined minimum length for changing the condition of said receiver from a higher to a lower degree of selectivity, a selector arranged under the control of said receiver, and means under the control of the selector for re-establishing the normal high selective condition of thereceiver.

may also f be applieduto 7 wireless transmission of selector impulses amplitude of th e In a telephone'system in combination,

a transmission line, means for transmitting signalling currents of voice frequency over said line, a signal receiver normally respon- 'sive to signals of predetermined minimum length,a selector arranged under the control nal receiver normally responsive to signals of predetermined minimum length, a selector arranged under the control of said receiver, means under the control of the selector for shifting the receiver from a more selective to a less selective condition, and other means under the control of the selector for re-establishing the normal condition, of high selectivity of the receiver. a a 5. A device for receiving voice frequency signals in-telephone plants comprising a rectifying device, a signal receiver normally responsive to rectified signals of predetermined minimum length, a selector arranged underthe control of said receiver, means nnder the control of the selector for shifting the receiver; from a more selective to a less selective condition, and other means under the control of said selector for re-establishthe. normal high selectivity of the reeeiver,

TORSTEN ,ADIL LUNDELL.

,TORBERN LAURENT. 

